The Project leader will continue studies to improve autologous bone marrow transplantation (BMT) therapy for CML and to characterize abnormal hematopoiesis in this lethal malignancy. In Specific Aim 1 in vitro studies will be performed on samples obtained from patients undergoing autologous transplant to assess the effect of high dose chemotherapy priming and mobilization on phenotype, number and preferential marrow or blood origin of benign primitive and committed hematopoietic progenitors. Clinically acceptable methods for large scale selection, expansion and retroviral marking of benign progenitors to be used in subsequent clinical autologous transplant trials incorporating both priming and ex vivo selection will be developed. In Specific Aim 2, a clinical t rial assessing the efficacy of autologous transplant after high dose cyclophosphamide will be continued. In subsequent trials, subsets of patients at high risk of relapse will receive autologous transplants combining high dose cyclophosphamide priming with infusion of hematopoietic cell subpopulations selected after priming and enriched for benign progenitors. The contribution of progenitors to early and late hematopoietic reconstitution and to relapse will be determined by retroviral marking studies. In Specific Aim 3 efficacy of autologous, IL2- activated natural killer (ANK) obtained from peripheral blood, expanded ex vivo and infused after autologous transplant to prevent recurrence of CML will be tested. In companion studies mechanisms underlying the observed suppression of CML progenitors by autologous ANK in vitro will be addressed. Over the proposed five year funding period, the Project Leader expects to develop modifications of the above described approach for benign stem cell selection and expansion which depend on progress in basic research studies described in Projects 1 and 2. The methods of autologous stem cell selection, expansion and transplantation developed in Project 2 will be useful not only for treatment of CML but for other lethal hematopoietic malignancies and solid tumors.